When Yale University psychology professor Laurie Santos set out to teach a new course on how to be happy, the reaction was stunning.

“Psychology and the Good Life,” which began this semester, is the most popular class in the history of Yale College, with more than 1,200 students enrolled, the Yale Daily News reported. One classroom wasn’t enough, so the lectures are now being simulcast around campus.

And now, the class will be available to anyone with an internet connection — for free. Online-education provider Coursera has teamed up with the Ivy League university to offer the entire course, including graded assignments, online starting in March. You can register here.

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No one is more surprised by the course’s popularity than Santos, who started the class to help students navigate stress, depression and other mental health challenges. But it’s not just young people who are looking for answers. The course hit a nerve well beyond Yale, with media clamoring to interview Santos about her lessons.

“Adults really are thinking about the things they can do to live a better life and become a bit happier,” Santos told TODAY.

“There’s a good answer for how to do this in the science of psychology. We know a lot about the kinds of things that really make us happy and stuff that doesn’t.”

Here are six of her happiness lessons:

1. Spend time and energy in the right way

We tend to strive for certain things we think will make us happy — a job with a big salary or perfect grades — when in practice, we don’t enjoy them as much as we think, Santos said.

We also spend hours on Facebook or Twitter, even though research suggests being on social media is associated with depression and anxiety, she added.

Overscheduled, distracted and glued to our screens, we’re missing out on things that do make us happy: real-life, face-to-face social connections with people you can see blush, smile and wink; and “time affluence” — just having free time, with nothing on the calendar to get in the way of your leisure.

2. Take time to express gratitude

Pausing for 10 minutes a day to think about five things you’re grateful forcan increase your appreciation of what matters and improve your well-being, Santos said.

“The big key is that when you do it, it can’t just be rote. It can’t just be, ‘My house, my spouse, my kids’ every day,” she noted. “You have to take time to feel it… it’s a moment to really reflect on, ‘What would my life be like without this thing?’”

Usually, the gifts in your life come from someone you’re thankful for, so really think about people who helped you.

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3. Do something nice for somebody else and talk with others

People who engage in random acts of kindness boost their well-being. That includes small gestures and bigger ones, like donating money to charity.

One of Santos’ favorite studies found people who spent money on others reported greater happiness, with such generosity bestowing a “warm glow” on the givers.

Another favorite study discovered that a simple act of connecting with a stranger — talking to somebody on a train or a plane, for example — can boost your mood. We underestimate other people’s interest in connecting, but such simple exchanges can be happy for everyone involved, researchers said.

4. Find some time to be mindful

Meditate for five or 10 minutes a day to increase well-being. You can go for any type of meditation you like — just schedule the time, sit down in a quiet spot, close your eyes and be in the present moment.

Santos likes to do a loving kindness meditation. She thinks about the people in her life she cares about and silently sends them wishes such as, “I want you to be happy, I want you to live well.” Such mantras help her feel a loving protection over her loved ones. You can also extend the wishes to all living beings.

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5. Get plenty of exercise and sleep

Exercise is not only good for your body, but your sense of well-being. It also decreases depression symptoms, Santos said.

Another simple thing you can do to feel better is to get as much sleep as you need, since sleep deprivation can diminish your mood, she added.

6. Practice these happiness behaviors every day

It’s like exercise: Just doing a couple of squats here and there won’t work. You have to keep working out to see results.

“Sometimes, you think you do these things once and you’re good and you’ll be happy forever, but that’s not the case,” Santos said.

“One of the major lessons that comes from this work is that changing your well-being is possible, but it takes a lot of work.”

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This article was updated Feb. 22 to include information about the free Coursera class.